Solar and pool heating in Perth: heat pump vs solar thermal vs solar PV

Perth's outdoor climate creates genuine value in pool heating. Extending a pool season by 3–4 months (September through November and March through May) is achievable with the right system. The choice between solar thermal collectors, a heat pump, and solar PV powering a heat pump has distinct cost, performance, and maintenance trade-offs.

The three approaches

1. Solar thermal collectors (roof collectors)

How it works: Black rubber or polypropylene tubing panels are installed on the roof. Pool water is pumped through the panels and heated by direct solar radiation. No electricity required for heating (only pool pump electricity).

Perth performance: Solar thermal collectors are well-suited to Perth's high solar radiation. A properly sized system (typically 80–100% of pool surface area in roof collectors) can extend the pool season significantly — heating to comfortable temperatures (26–30°C) during September–November and March–May.

Cost:

• Installation: $2,500–$6,000 for a 40–60m² pool
• No ongoing energy cost beyond pump electricity
• Lifespan: 10–20 years (rubber collectors) or 20–30 years (polypropylene)

Limitations:

• No heating during cloudy periods or winter (insufficient radiation)
• Heating only when sun is on the collectors
• Cannot heat to high temperatures on demand
• Requires suitable north-facing roof area for collectors

2. Pool heat pump

How it works: A heat pump extracts heat from ambient air and transfers it to pool water. Works on the same principle as a reverse cycle air conditioner — COP (coefficient of performance) typically 5–7, meaning 1kW of electricity produces 5–7kW of heating.

Perth performance: Heat pumps work well in Perth's mild winters. Even on a 15°C winter morning, a heat pump with COP of 5 produces 5kW of heating from 1kW of electricity. COP increases as ambient temperature rises — on a 25°C day, COP may reach 7–10.

Running cost (at A1 33.26c/kWh):

• A 12kW heat pump drawing 2.2kW (COP ~5.5) heats a medium pool (50,000L) from 18°C to 28°C in approximately 24–36 hours
• Running continuously for 12 months at 4 hours/day: approximately 2.2kW × 4h × 365 = 3,212kWh/year × 33.26c = $1,068/year
• On Midday Saver super off-peak (8.85c/kWh): $1,068 × (8.85/33.26) = $284/year (running 9am–3pm)

Cost:

• Installation: $3,500–$7,000
• Annual running cost: $300–$1,200/year depending on tariff and hours

Advantages:

• Heats to any target temperature (25–35°C)
• Works at night and in overcast conditions
• No roof space required

3. Solar PV powering a heat pump

How it works: Your existing solar panels generate electricity during the day. The pool heat pump is scheduled to run during solar generation hours (typically 9am–3pm), self-consuming solar electricity rather than importing grid power.

Perth economics: At A1, self-consuming solar avoids 33.26c/kWh of grid import. This is substantially better than the 2c/kWh DEBS off-peak export rate. Powering the heat pump from solar self-consumption makes pool heating effectively free (using solar that would otherwise export at 2c/kWh).

Setup:

• Timer on pool heat pump: set to run 10am–3pm
• Or: smart pump controller that activates when solar export begins
• Heat pump maintains pool temperature passively when pump isn't running

Solar coverage: A 6.6kW solar system generating 30kWh on a clear summer day, with a household base load of 10kWh daytime, has 20kWh of surplus available for export or self-consumption. Running a 2.2kW heat pump for 5 hours uses 11kWh — well within available surplus.

Winter consideration: In winter (June–July), Perth solar generation is lower and the heat pump needs more energy to heat against cooler ambient temps. Winter pool heating with solar self-consumption may require grid top-up on cloudy days.

Comparison table

| System | Capital cost | Annual running cost (Perth pool) | Heating season | Control | |---|---|---|---|---| | Solar thermal | $2,500–$6,000 | ~$50–$100 (pump electricity only) | Spring/Summer/Autumn | Day only, sun dependent | | Heat pump (A1 tariff) | $3,500–$7,000 | $600–$1,500/yr | Year-round | Full control | | Heat pump (Midday Saver 8.85c) | $3,500–$7,000 | $160–$400/yr | Year-round (daylight operation) | 9am–3pm | | Solar PV + heat pump (self-consume) | $0 extra if solar exists | ~$0 marginal cost | Year-round (daylight) | Solar hours |

What's right for a Perth pool?

For a household without solar: A heat pump on Midday Saver (9am–3pm at 8.85c/kWh) is the most cost-effective heating system. Capital cost $3,500–$7,000, annual running cost $160–$400.

For a household with solar and surplus midday generation: Solar PV self-consumption driving an existing or new heat pump is effectively free heating during solar hours. This is often the strongest economic case — zero marginal running cost using surplus solar that would otherwise export at 2c/kWh.

For a household prioritising minimal capital cost: Solar thermal has the lowest long-term running cost if a north-facing roof section is available. Limited to spring/summer/autumn.

Combination approach: Some Perth pools use both solar thermal (for shoulder seasons when sun is sufficient) and a heat pump backup for winter or cloudy periods. The heat pump acts as a supplement rather than primary heating.

Pool pump optimisation for solar homes

The pool circulation pump is a separate load from the heater — it runs continuously (4–12 hours/day for filtration) and uses 250W–2kW depending on pump type.

Variable speed pump: A variable speed pump (VS) can run at low speed (200–400W) for filtration and high speed (1–2kW) for backwash. Scheduling low-speed filtration during solar hours (9am–4pm) means the pump is largely solar-powered on a 6.6kW system.

Standard single-speed pumps (fixed ~1kW) running continuously are a significant electricity cost. Replacing with a VS pump pays back in 3–5 years and reduces pool running costs by 50–70%.

Your pool's heating requirements depend on pool size, desired temperature, and season. Upload your Synergy bill to BillWise to see how much of your electricity cost is attributable to pool equipment and model the savings from Midday Saver timing.